` ``If 1=sum(not({A,B,C,D...`

To determine which one is zero:

` ``1+sum(not(cumSum(not({A,B,C,D...`

For example, with two variables it would be

` ``a xor b`

If I wanted to test exactly one of a, b, c, … were 0, would it be

` ``a xor b xor c xor...`

or would I need parenthesis somewhere? ]]>